Wednesday, January 10, 2018

Short-stem humeral components, an advantage?

The authors suggest that short-stem press-fit humeral components have recently been developed in an effort to preserve bone in shoulder arthroplasty. They state "traditional-length humeral stems may be associated with stress shielding. In an effort to seek bone preservation and more closely mimic native bone stresses, short-stem press fit humeral components have been developed. Whereas studies have demonstrated that stemmed humeral component loosening is a less significant concern compared with glenoid component loosening, concern still exists that modern short stem and stemless humeral components may ultimately loosen. However, the utility of these implants is advantageous, given the associated complications of stemmed humeral components, such as stress shielding, and also the complications of revision stemmed humeral arthroplasty, such as fracture and proximal humeral bone loss."

Their review of the literature included a recent report evaluating the clinical and radiographic outcomes of 73 TSAs performed with a collarless press-fit short stem demonstrating a 71% rate of radiolucent lines. The overall revision rate at a mean of 33 months was 12%, and 8.7% of the remaining stems were considered at risk for loosening. Another article reported radiolucencies in 22% of 49 short-stem TSAs with a press-fit collared design.

They conducted a multicenter retrospective review of 64 patients receiving an anatomic short-stem humeral component with two year followup. The Simple Shoulder Test scores improved from an average of 4 to 10 (P < .001). On radiographic examination, 9% stems were deemed at risk for loosening, but there was no gross loosening in any patient.

Comment: There is a real opportunity to compare short-stemmed humeral components to standard stems implanted with impaction autografting with respect to (1) clinical outcomes, (2) revision rates, (3) fracture rates, (4) the amount of bone removed at the time of the procedure, and (5) the amount of bone loss due to stress shielding.

Here are the x-rays of the right and left shoulders 10 years after implantation of standard length humeral stems with impaction grafting showing minimal bone loss and no stress shielding.

and here are the x-rays of recently reported short stems at two years postoperatively suggesting stress shielding proximal to the point of the diaphyseal press fit (arrows).